Comparison of three different correction trajectories for foot and ankle deformity treated by supramalleolar...

Based on the principle of distraction osteogenesis, external fixators are widely used in deformity correction of the foot and ankle. In this study, a novel ankle external fixator is proposed to correct complex multiplane deformities, especially for supramalleolar osteotomy to correct distal tibia deformities. The relatively simple structure and fewer struts in the proposed fixator reduce the complexity of adjusting the external fixator. Based on two existing adjustment strategies, a new strategy taking into account the orientation and shortest path of the ankle joint center is proposed, which is named joint adjustment for equal bone distraction. By proposing the inverse kinematic solutions of the novel external fixator, mathematical derivations of the bone trajectory and modelling of the bone shape for the three distraction strategies are performed. The results obtained by comparative analysis indicate that a uniformly spaced path of the ankle joint center can be acquired, and a smooth and uniform correction trajectory of the distal tibia end can be obtained using the new adjustment strategy. It can avoid bone end interference and only generates a maximum deviation 0.66% greater than the currently optimal 1 mm/day. The new strategy can perform multiplane corrections simultaneously, which shortens the correction time and reduces the patient's pain.